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"Low Noise Electronic Design," Motchenbacher and Fitchen, 1973

Posted: Wed May 08, 2019 5:35 pm
by mediatechnology
"Low Noise Electronic Design," "Design with Feedback," Section 7-4, C.D. Motchenbacher, F.C. Fitchen, 1973.

The "op amp around the transistor" "current feedback" circuit shown by Demrow in 1968 https://proaudiodesignforum.com/forum/p ... =12&t=1052 and documented by Motchenbacher and Fitchen in 1973.
This is the single-ended half-circuit of the popular "Cohen" differential style preamp.


Image
"Low Noise Electronic Design," "Design with Feedback," Section 7-4, C.D. Motchenbacher, F.C. Fitchen, 1973. Figure 7-3.

Note the common base connection (figure 7-3a) with "current feedback."

"Low Noise Electronic Design," "Design with Feedback," Section 7-4, C.D. Motchenbacher, F.C. Fitchen, 1973. https://proaudiodesignforum.com/images/ ... on_7-4.pdf

Re: "Low Noise Electronic Design," Motchenbacher and Fitchen, 1973

Posted: Thu May 09, 2019 11:02 am
by JR.
Page 124... 8-)

I've shared this story before... back in the late 70s I was living about one town away from Bridgeport where Fitchen was teaching at University of Bridgeport. His phone number was in the phone book so I called him. I wanted to pick his brain about a Leach low noise topology that was unusual (he didn't know either). After a nice chat he asked me to contribute to a chapter for his next book... I demurred, I was not an academic (college dropout), but I gather Motchenbacher was also a working design engineer, and Fitchen was the professorial half of the team.

JR

Re: "Low Noise Electronic Design," Motchenbacher and Fitchen, 1973

Posted: Thu May 09, 2019 12:35 pm
by mediatechnology
Thanks John for that story.
Yes, page 124.

I had posted that page here elsewhere but I thought it deserved its own thread and index.
Its one of the more practical books and I enjoyed leafing through it again.

You don't see the common base circuit often unless its a mic preamp re-purposed as a bus summing amp or "current input" moving coil phono preamp.

Re: "Low Noise Electronic Design," Motchenbacher and Fitchen, 1973

Posted: Sat May 11, 2019 3:04 pm
by JR.
Yup we live in the time of "Bridging" input terminations that favor high Z.

MC is low Z source but even I tried to present a 10x termination impedance... but that was a very long time ago.

JR